Cathode-ray signal-translating device



Oct. l, 1968 J. BURNS CATHODE-RAY SIGNAL-TRANSLATING DEVIGE OriginalFiled Dec. 4, 1961 MULTI VI BRATOR United States Patent O 3,404,308CATHODE-RAY SIGNAL-TRANSLATING DEVICE Joseph Burns, iequannoclr, NJ.,assigner to Fairchild Camera and instrument Corporation, a corporationof Delaware @riginal application Dec. 4, 1961, Ser. No. 156,627. Dividedand this application May 20, 1966, Ser. No. 551,769

2 Claims. (Cl. 315-12) ABSTRACT F THE DISCLQSURE A cathode-raysignal-translating device includes airst target comprising a thin glasssubstrate having a phosphor screen adhering to one side and a layer ofphotoemissive material, for example a photocathode of a caesium-antimonyor silver-caesium alloy on the other side. A conventional electron gunand deflection system scans the phosphor screen with a signal-modulatedcathode ray which causes the photocathode to develop a space-modulatedelectron beam representative of the input signal. The device furtherincludes a barrier grid assembly disposed adjacent a target comprising aconductive plate on which is disposed a continuous layer of dielectricmaterial having a substantial secondary electron emission ratiocharacteristic. interposed between this barrier grid assembly and thephotoemissive layer is a collector electrode. A multivibrator isprovided for shifting the potential of `the conductive plate between twodesired potential levels. During application of a positive potential tothe conductive plate, the electron beam from the photoemissive cathodeis effective to write on the dielectric layer of the barrier gridassembly. When a negative poftential is applied to the conductive plate,the charge pattern on the dielectric layer is read out by scanning thefirst target with a beam from the electron gun.

This is a division of application Ser. No. 156,627, filed Dec. 4, 1961,now abandoned.

This invention relates to cathode-ray signal-translating devices and,while it is of general application, it is particularly applicable toso-called scan converters, that is, devices of the type including astorage target on which information is stored by a write gun and fromwhich such information is derived either simultaneously or sequentiallyby a read gun.

In the conventional scan converter, a storage grid or target is scannedby a cathode-ray beam from the write gun and, through the process ofbombardment induced conductivity, there is developed a charge pattern onthe storage grid. If the storage grid is then scanned by a relativelylow-potential reading cathode-ray beam, the backing electrode of thestorage grid draws a capacitive current varying in accordance with thecharge pattern as the read gun beam brings `the successive elementalareas of the target electrode to a uniform potential substantially thatof the read gun cathode or the collector, depending upon the primarybeam velocity, at the same time erasing the storage pattern. Thescanning of the storage grid by the reading beam may be eithersimultaneous or sequential, that is, after one complete block ofinformation is stored by the write gun, the read gun scans the storagegrid to reconstitute the stored block of information.

Scan converters of the type described are frequently used to storehigh-frequency periodic information or highspeed transient informationwhich can then be read out at a slower rate more compatible with thedesired use to be made of the information. To permit high-speed writing,the write beam must have a high energy level,

3,404,38 Patented Oct. 1, 1968 that is, it must have a high density anda high accelerating voltage in order to store a significant amount ofenergy in each elemental area of the storage grid as it is rapidlyscanned. However, it is well known that maximum secondary electronemission occurs between the first and second crossover points on thepotential-secondary emission characteristic of the particular material,which, for the most efficient dielectric materials useful on the storagegrid, occurs at a relatively low potential of the order of a few hundredvolts. Thus, in prior scan converters, the accelerating voltage of theWrite beam has been a compromise 'between these two conflictingcriteria.

In the present invention, the foregoing compromise is avoided byproviding two electron-optical transducers in cascade, effectivelydividing the former method of forming a charge pattern on the storagegrid into two steps each performed at optimum energy levels.

In accordance with the invention, there is provided a cathode-raysignal-translating device comprising an electro-luminescent firsttarget, an electron-gun assembly for generating a focusedsignal-modulated cathode ray, means for scanning such first target withsuch cathode ray to form thereon a luminous representation of thesignal, a layer of photoemissive material disposed closely adjacent suchfirst target, a barrier grid assembly including a conductive platehaving an adhering continuous layer of dielectric material and a gridnear such dielectric layer, and means for transferring to the suchdielectric layer the charge pattern developed on such photoemissivelayer by the scanning of the first target. The signal-translating devicefurther comprises a collector electrode means adjacent the dielectriclayer, and means for scanning the photoemissive target with aconstant-intensity, constant velocity cathode ray sequentially with thescanning thereof by the signal-modulated ray, whereby the collectorelectrode means reads off the charge pattern on the dielectric layer.The term signal-modulated cathode ray is used herein vand in theappended claims to refer to a cathode-ray beam modulated in intensityand having a constant defiection pattern or such a beam of constantintensity having a modulated scanning pattern. The term electro-opticalresponsive material is used herein and in the appended claims to referto a material having an electrical property variable wit-h illumination,for example a photoemissive or a photoconductive property.

For a better understanding of the present invention, together with other4and further objects thereof, reference is had to the followingdescription, taken in connection with the accompanying drawing, whileits scope will be pointed out in the appended claims.

Referring now to the drawing:

FIG. 1 is a schematic representation of an embodiment of the inventionin a scan converter utilizing a photoemissive material in place of aphotoconductive material, while.

FIG. 2 is a schematic representation of the embodiment `of a modifiedform of the invention in a scan converter tube utilizing a singleelectron gun for writing and reading sequentially.

Referring now more particularly to FIG. 1 of the drawing, there isrepresented a cathode-ray signal-translating device responsive to ahigh-frequency wave signal. This device comprises an electroluminescenttarget which may be in the form of a thin transparent supporting member1f), for example a thin plate of glass or a plate-like assembly ofoptical fibers. The member 10 has a layer 11 of electroluminescentmaterial, such as a suitable phosphor, adhering to one face of the plateand preferably having an electron transparent conductive coating 12 inthe form of a conventional aluminized backing overlying the phosphorlayer 11. The other surface of the supporting member 16 has an adheringtransparent conductive coating 45 on which is disposed a layer 4@ ofphotoemissive material of any Well-known type, for example acaesium-antimony or silver-caesiurn alloy.

The device of FIG. l also includes an electron-gun assembly fo-rgenerating a focused signal-modulated cathode ray. This electron-gunassembly includes the unit shown schematically as 13 comprising theusual cathode, control electrode, and accelerating electrodes forming anelectrostatic focusing means. Alternatively, magnetic focusing means maybe used if desired. There is also provided means for scanning the targetwith the cathode ray to form thereon a luminous representation of aninput signal, This scanning means may be in the form of a series ofspaced pairs of plates 15551, 141), and 14C adapted to be connected tothe signal input source 17 through a conventional delay line 18terminated in a resistor 19 having a value equal to the characteristicimpedance of the l-ine. The plates 14a, Mb, and 14E-c are connected tosuitable taps on the delay line 18 so located that the signals appliedto the successive plates are delayed by intervals approximately equal tothe transit time of the cathode-ray beam between the plates.

The cathode-ray device of FIG. l includes also an electron-chargestorage target in the form of a grid or mesh 41 coated with a suitabledielectric material capable of emitting secondary electrons, for examplemagnesium tiuoride. The device also includes means for transferring tothe target electrode 41 the charge pattern developed on thephotoemissive layer 40 by the scanning of the phosphor layer 11. Thismeans may be in the form of an accelerating grid or mesh electrode d2disposed near the photoemissive layer 46, that is, between the targetcomprising the elements 11, 12, dit and the storage target 4l. There isalso provided a decelerating grid electrode 43 disposed adjacent thestorage grid 41 and between it and the electron-gun unit Z3 and acoliimating electrode in the form of an annular conductive ring te forcollimating the cathode-ray beam from the electron gun 23 during thescanning of the targets as described. The accelerator electrode 42 maycomprise also a collector for deriving an output signal varying with thecharge pattern on the storage grid target 41 as it is scanned by thecathode-ray beam from the electron gun Z3. To this end, the acceleratorelectrode ft2 is connected to a suitable potential such as +500 V.through a load resistor 45 to which is connected an output terminal 45a.The conductive element of the storage grid t1 is adapted to beselectively connected via a switch 41a to a potential approximately v.above the potential of the layer dit), that is about +40 v., to apotential about 300 v. above that of the layer 40, that is about 320 v.,or to approximately the potential of the layer 46, for example toground, as illustrated. The decelerator grid S3 and the collimatingelectrode i4 are connected to adjustable taps on a voltage-dividerresistor 15 connected across a suitable source -l-O v. If desired, amagnetic lens (not shown) may be disposed between the photoemissivelayer and the storage target 41 to facilitate the transfer of the chargepattern without distortion.

The potentials applied to the several electrodes of the device of FIG. 1will depend upon its particular design parameters and, to an extent,upon its intended use. However, typical electrode potentials may be ofthe order of those indicated in the drawing.

The operation of the cathode-ray signal-translating device of FIG. l maybe as follows: Assume that the conductive element of the storage grid 41is initially adjusted to approximately 20 v. above the potential of thephotoemissive layer 40, that is, below the first crossover point on thesecondary emission ratio characteristic 0f the storage grid 41. Thephosphor layer 11 is then scanned with a defocused raster of constantintensity to bring the potential of the surface of the storage grid 41to equilibrium potential. The potential of the conductive element d, ofthe storage grid 41 is then increased to approximately 300 v, above thatof the photoemissive layer 40 and the information to be translated isutilized to Write on the phosphor layer 11 as described above. Theelectron pattern formed on the photoemissive layer 40 is transferred tothe surface of the storage grid 41 by the accelerating grid 42 duringthe scanning process and, due to the fact that the dielectric layer ofthe storage grid l1 is above the second crossover p-oint on thesecondary emission ratio characteristic, each elemental area of thephotoemissive layer d@ which is caused to emit electrons produces acorresponding positively charged area on the storage grid 41. Y

In order to retrieve the information represented by the electron patternon the photoemissive layer 455, the conductive element of the storagegrid 41 is then `reduced substantially to the potential of thephotoemissive layer 40 as it is scanned Vwith the focused nonmo-dulatcdcathode-ray beam from the electron gun 23. The electron charge Apatternnow existing on the storage grid l1 is such that it permits the flow ofelectrons from the scanning beam in those areas which have becomepositively charged, as described above, and repels such electrons inother areas. The electrons from the scanning beam of the electron gun 23passing through the storage grid 41 are collected by the acceleratingelectrode 42 and develop an output signal across the load resistor 45which appears at output terminal 45a.

The cathode-ray signal-translating device of FIG. l has a number ofadvantages. The formation of the input signal wave form on the phosphorlayer 11 may be at an extremely high speed, considerably greater thanthat possible in prior scan converter tubes, due to the substantialenergy in the high-density cathode-ray beam from the gun 13 operatingwith a high accelerator potential. As pointed out above, such a highaccelerator potential could not be applied directly to the storage gridd1 because of secondary electron emission effects. The speed of Writingthe input signal on the phosphor layer 11 may be so high that it couldnot be utilized if it were attempted to apply it directly to otherutilization circuits. However, by storing on the storage grid 41 thisinformation Written at high speed on the phosphor layer 11, it may thenbe retrieved by relatively lower speed scanning of the grid 41 by theelectron gun 23 for utilization in any convenient manner. Furthermore,by thus providing separate electrode elements for writing and reading,the optimum potentials for the two functions may be selectedindependently, thus resulting in a very much higher efficiency in theover-all signal-translating device and providing a gain in the electronamplier comprising the photoemissive layer 40 and the storage grid 41.

Turning now to FIG. 2, there is represented a modified form of theinvention for utilizing the information formed as an electron pattern onthe photoemissive layer 40 of FIG. 1. In this arrangement, there isprovided a barrier grid assembly comprising a grid or mesh electrode 47disposed adjacent a target comprising a conductive plate 48 on which isdisposed a continuous layer 49 of dielectric material having asubstantial secondary electron emission ratio characteristic. Interposedbetween the target 48, 49 and the photoemissive layer 40 is a collectorelectrode in the form of a cylindrical conductive element 5?. Theconductive plate 48 is connected to means for shifting its potentialbetween two desired potential levels. This may be in the form of amultivibrator 51 having an output Wave of the form represented in thecurve 52. The collector electrode 50' may be connected to a suitablesource, such as v., through a load resistor 53, the output signal beingtaken from across the load resistor 53 and appearing at an outputterminal 54. ln this embodiment of the invention, the same cathode-raybeam from the electron gun 13 is utilized both for writing and reading.

The operation of the barrier grid form of the invention illustrated inFIG. 2 is as follows: The barrier grid 47 adjacent the surface of thedielectric layer 49 acts both as a collector electrode, in addition tothe collector 50, and establishes an equilibrium potential on theadjacent surface of the dielectric layer 49. It also prevents coplanargrid effects and prevents electron redistribution on the surface of thedielectric layer 49.

Initially, equilibrium potential on the surface of the dielectric layer49 is established at l or 2 volts positive with respect to the barriergrid 47 which creates a negative barrier when the surface of thedielectric layer 49 tends to rise higher. A positive potential appliedto the conductive plate 48 capacitively shifts the potential of thesurface of the dielectric layer from its equilibrium value inpreparation for writing. For example, if a positive pulse fromY themultivibrator 51 is applied to the conductive plate 48, the potential ofits surface will shift positively by an equal amount due to capacitivecoupling. Electrons from the photoemissive layer 40, as the phosphorlayer 11 is scanned by the writing gun, can now land on the surface ofthe dielectric layer 49 in accordance with the modulation of the writegun beam. The written areas on the surface of the dielectric layer 49are thus restored to its previous equilibrium potential.

After the input signal has been stored on the dielectric surface 49 byone scansion of the writing beam, a negative pulse from themultivibrator 51 is applied to the conductive plate 48, returning itssurface to its original equilibrium potential by capacitive coupling.The charge pattern previously established during the writing cycle maybe retrieved by again scanning the target 11, 40 with a beam from theelectron gun 13 now operating as a constant-intensity read gun. Theresulting constantintensity electron emission from the photo-emissivelayer 40 now effectively scans the surface of the dielectric layer 49,returning the potential of the written areas to their equilibrium valueand producing a secondary electron emission output modulated inaccordance with the previously written information, which output iscollected by the collector electrode 50, and producing an output signalacross the load resistor 53 which may be derived from the outputterminal 54. It is noted that the read-out, as described, is destructiveof the charge pattern on the surface of the dielectric layer 49 formedduring the writing cycle.

While there have been described what are, at present, considered to bethe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. A cathode-ray signal-translating device comprising:

an electroluminescent target;

a first electron-gun assembly for generating a focused signal-modulatedcathode ray;

means for scanning said target with said ray to form thereon a luminousrepresentation of the signal;

a layer of photoemissive material disposed closely adjacent said target;

a barrier grid assembly including a conductive plate having an adheringcontinuous layer of dielectric material and a grid near said dielectriclayer;

means for transferring the charge pattern from said photoemissive layerto said dielectric layer;

collector electrode means adjacent said dielectric layer;

and means for scanning said target with a constant-intensity,constant-velocity cathode ray sequentially with the scanning thereof bysaid signal-modulated ray, whereby said collector electrode means readsoff the charge pattern on said dielectric layer.

2. A cathode-ray signal-translating device comprising:

an electroluminescent target;

a first electron-gun assembly for generating a focused signal-modulatedcathode ray;

means for scanning said target with said ray to form thereon a luminousrepresentation of the signal;

a layer of photoemissive material disposed closely adjacent said target;

a barrier grid assembly including a conductive plate having an adheringcontinuous layer of dielectric material and a grid near said dielectriclayer;

means for transferring the charge pattern from said photoemissive layerto said dielectric layer;

collector electrode means adjacent said dielectric layer;

means for scanning said target with a constant-intensity,constant-velocity cathode ray sequentially with the scanning thereof bysaid signal-modulated ray, whereby said collector electrode means readsOff the charge pattern on said dielectric layer;

and means for switching the potential of said conductive platesynchronously with scanning means to determine whether a charge patternis formed or erased on said dielectric layer.

References Cited UNITED STATES PATENTS 2,879,442 3/1959 Kompfner et al.315--12 2,916,661 12/1959 Davis 315--12 X 2,919,377 12/1959 Hanlet315--12 3,165,664 1/1965 Callick 315-12 RODNEY D. BENNETT, PrimaryExaminer.

M. F. HUBLER, Assistant Examiner.

